Instructions The Sponge: Scoop 1 cup of starter into a large ceramic mixing bowl. Add the warm water and 3 cups of the flour. Beat vigorously. Cover this Sponge with plastic wrap and put it aside to work. This period can be very flexible, but allow at least 2 hours, and up to 8 hours. A longer period (at a lower temperature) will result in a more Sour flavor. The dough: When the sponge has bubbled and expanded, blend in the salt, sugar (if using) and remaining 2 cups of flour. Mix until the dough comes together then turn it out onto a floured board and knead it for 3 to 4 minutes. Give it a rest while you clean and grease the bowl. Continue kneading for another 3 to 4 minutes, adding extra flour as needed, until dough is smooth and elastic. Add only enough extra flour to keep dough from sticking. Place the dough in the bowl, cover and let it rise until doubled (1 to 2 hours). Shaping and Baking: Turn the dough out, knead briefly then divide in 2 halves. Shape halves into 2 loaves, cover and let them rise until doubled (this can take up to 2 hours). Slash the tops and place on a lightly greased, cornmeal sprinkled baking sheet. Bake in a preheated 450F oven for approximately 20 minutes, until golden brown. Sourdough breads sometimes don’t brown well. To promote browning, brush loaves with vegetable oil about 10 minutes before the end of the baking time.